1. Field of the Invention
The present invention relates to a motor-driven steering assist apparatus.
2. Description of the Related Art
In a motor-driven steering assist apparatus of a rough road traveling vehicle, such as a buggy vehicle or the like, as described in Japanese Patent Application Laid-open No. 2004-336565 (patent document 1), there is a structure which is interposed between a steering wheel and a tire wheel side steering member, which assists steering force applied to the steering wheel by a driver on the basis of torque generated by an electric motor.
The motor-driven steering assist apparatus in the patent document 1 has the following elements. A single unit body covered by first to third housings, an input shaft to which a steering wheel is connected, an output shaft to which a wheel side steering member is connected, and a torque sensor which is provided between the input shaft and the output shaft. An electric motor is driven in correspondence to a detected torque of the torque sensor, a worm gear is coupled to a rotary shaft of the electric motor, and a worm wheel is coupled to the output shaft and is engaged with the worm gear built-in. Further, an upper end portion of the input shaft and the torque sensor are supported to the first housing. An upper end portion of the output shaft, the electric motor, the worm gear and the worm wheel are supported to the second housing. A lower end portion of the output shaft is supported to the third housing, and the second housing can be attached to a vehicle body frame (a vehicle body side bracket).
In the motor-driven steering assist apparatus in the patent document 1, an attaching boss provided in the second housing is directly fixed to a support portion of a vehicle body side attaching stay.
There is a risk that vibration from a road surface and an engine when the vehicle travels is transmitted to the torque sensor within the first housing via the vehicle body side attaching stay through the second housing, whereby the torque sensor produces an improper operation due to the vibration along an axial direction of the input shaft and the output shaft.